British light-heavyweight Buatsi earned a win yet underwhelming start to life under new promoters with a points victory over Parker in Manchester.
The Olympic bronze medallist's work rate seemingly secured him a judges' verdict in a competitive 10-round fight at the Manchester venue.
But the challenger had his moments, delivering effective single shots in a contest where the techniques failed to mesh, with frequent clinching spoiling the action.
The officials had it 96-94 to the winner, with the final judge a even score.
"It wasn't my finest display but what defines champions? They prevail," Buatsi stated in the arena as he was greeted with negative reactions from the crowd.
The British fighter got back to winning after his maiden career setback - an memorable fight with Callum Smith in last winter - to secure a 20th career victory.
Various analysts thought Parker, thirty-one, merited the decision but the British boxer endured the second loss of his 28-fight career.
The Champion Claims Triumph in Dull Affair
The fighter's advancement has plateaued in recent years through promotional disputes and considerable time of lack of fights.
Once tipped as the next star of UK boxing, he now stands trying to realize his potential - possibly in what seems like a last chance - under new promotional backing.
He began cautiously, with neither fighter prepared to take risks in a calculated initial rounds.
The challenger, whose single earlier setback came at super middleweight against his former opponent in two years ago after damaging his hand mid-fight, was participating in his second bout at light heavyweight.
By the fight's midpoint, Parker had kept it close, making life awkward for the favorite, who utilized a protective stance to barely take the cleaner rounds.
The spectators' acceptance decreased during constant clinching, with the challenger falling to the floor several times during grappling.
The underdog finished the stronger, but many rounds were challenging to assess. Although, former world champion the boxing analyst - commentating on the broadcast network - had it significantly in favor for Parker, scoring for Buatsi just one round.
Buatsi progresses, but with the caliber of power puncher Benavidez, and Eastern European fighter Bivol dominating the weight class, the journey to titles - on this evidence - still looks steep.
Hatton Memorial Inspires Local Rivalry Contest
In the co-main event, Arthur defeated Bradley Rea by split-decision in a excellent Manchester vs Manchester battle to capture the European light heavyweight title.
The arena became quiet for a extremely emotional tribute ahead of the contest as a bell ceremony tolled in memory of the city's native Ricky Hatton, who died aged 46 in last month.
It was the premier televised boxing event in the city since the passing of Hatton. As the final chime ended, the quiet became a chant of "only one Ricky Hatton".
The action within the ring equaled the feeling. The eventual winner was floored by a left hook flush on the chin in the second round, rising shakily to his footing on the count of eight.
But the red-colored attire of Arthur soon came forward again. From the other corner, the opponent - in opposing blue - was injured quickly, heavy swelling forming under his orbital area as the pair exchanged hard punches.
Rea, 27, connected with strong blows but the champion, thirty-four, fought fire with fire with powerful upward punches as the intensity hardly diminished over 12 rounds.
The victor narrowly won the result with judges scorecards of even score, 115-113 and clearer margin, but both fighters were determined and full of heart, exactly what their idol the legend represented.
